The inferior heavy oil is rich in polycyclic aromatic hydrocarbons, it has high carbon hydrogen ratio, viscosity and density as well as excessively high content of sulfur, nitrogen, oxygen, residual carbon, heavy metals and mechanical impurities, and exhibits the resource characteristics such as being prone to condense and chars formation, which presents a significant challenge to the conventional processing routes of heavy oil. Most of the existing heavy oil processing technologies are difficult to meet the requirements of efficient and clean “chemical type” processing. The delayed coking is currently the preferred technology for disposing the inferior heavy oil, but it confronts with many challenges such as high output of inferior high-sulfur char, low yield of coking wax oil, difficulties in carrying out the “chemical type” processing, environmental pressure resulting from emission of large amount of volatiles, and potential safety hazard of shot chars. The catalytic cracking and hydrocracking technology for processing inferior heavy oil suffers many difficult problems such as low conversion rate, poor selectivity and low yield of olefin product, rapid deactivation and excessive consumption of catalyst, poor stability of the cracking device and excessively high processing costs; the solvent deasphalting technology used for processing inferior heavy oil faces with many problems, for instance, low yield of deasphalted oil, complicated “chemical type” processing, the highly efficient utilization of large-scale hard asphalt becomes the bottleneck of its industrialization. The technology of hydrogenation in suspended bed for the processing of heavy oil can theoretically meet the requirements of efficient and clean pretreatment of inferior heavy oil, But it has the characteristics of low conversion rate, high hydrogen consumption, low removal rate of heavy metals, the problems concerning tail oil processing and low-cost hydrogen source demand a prompt solution, and there are still some defects in the processing technology and equipment matching, thus it has not been put into large-scale industrial application successfully; in addition, the hydrogenated wax oil needs the secondary processing to achieve the “chemical type” processing, and the reciprocating cycle of hydrogenation and dehydrogenation during the process results in an excessively high energy consumption and poor economic performance.
Although many new technologies for the production of a variety of low-carbon olefins by catalytic cracking of heavy oil have been developed in China and foreign countries in recent years, for example, the DCC/CPP process developed by the SINOPEC Research Institute of Petroleum Processing (RIPP), the PetroFCC process developed by the Universal Oil Products (UOP) Company in the United States of America (USA), the HS-FCC process and THR process developed by the Japan Petroleum Energy Center, the TCSC process developed by the German Institute of Organic Chemistry, the INDMAX (UCC) process developed by the Indian Oil Corporation, the Maxofin process jointly developed by the Exxon Mobil and the Kellog Corporation, and the two-stage riser catalytic cracking (TMP) process proposed by China University of Petroleum (CUP), the new technologies have attracted extensive attention and pilot applications as demonstration projects in the petrochemical industry. However, due to the adaption and matching requirements between the structural properties of acidic molecular sieve catalysts and the heavy oil macromolecules, the current catalytic cracking of the inferior raw materials such as atmospheric residue oil, vacuum residue oil and deasphalted oil for preparing olefins suffers from a small pore structure of the catalyst, the diffusion of large heavy oil molecules in the process of mass transfer is subject to restriction, the molecules are difficult to enter the interior of the molecular sieve for performing the shape selective cracking. In addition, the strong hydrogen transfer performance of the acidic molecular sieve results in that the improvement scopes of the yield and selectivity of the olefins are limited; the molecules aggregated on the surface of the molecular sieve are prone to be excessively cracked under the action of the acidic center, it causes the poor product distribution or the occurrence of coking and condensation, thereby blocking pore channels of the catalyst. The currently used industrial and shape selective catalysts facilitates catalytic cracking of the inferior raw materials such as atmospheric residue oil, vacuum residue oil, deasphalted oil for preparing the low-carbon olefins. However, the cracking process suffers many problems, such as catalyst poisoning, poor atomization effect, large production of petroleum char, significantly reduced conversion rate and selectivity, thus the further development and optimization are urgently needed.
The calcium aluminate catalyst is an alkaline inorganic compound synthesized from the calcium oxide-based and alumina-based powder materials; the catalyst has strong alkalinity, high hardness, high melting point and desirable abrasive resistance, and may resist high temperature, water vapor and heavy metal pollution; the catalyst lacks the hydrogen transfer effect and can greatly improve the selectivity of pyrolyzed olefins; the strong dehydrogenation performance enables the hydrogen radicals to inhibit polycondensation of the pyrolyzed aromatic hydrocarbon radicals in the heavy oil, reduce char formation, thereby significantly improve the yield of liquid cracked from the heavy oil; in addition, it can promote the coking combustion or gasification regeneration reaction of the spent catalyst to be regenerated, and lower the regeneration temperature, thus it is a catalyst for cracking and chemical processing of heavy oil with great application potential. However, the calcium aluminate catalyst at present is mainly synthesized by high-temperature solidus reaction, the catalyst lacks a pore structure, and it has small surface area and large specific gravity, thus it is difficult to maximize the advantages that the alkaline catalyst may inhibit char formation and enhance selectivity of olefins, the lack of pore structure has become a bottleneck of an industrial application of the calcium aluminate catalyst.